1. Field of the Invention
The present invention relates to a recording/reproducing apparatus that uses an optical disc as a recording medium, more particularly, to a recording/reproducing apparatus capable of carrying out a focus bias adjustment and an aberration correction and an adjustment method therefor.
2. Description of the Related Art
A recording/reproducing apparatus that uses an optical disc as a recording medium generates, when laser light is irradiated onto a data recording surface of the optical disc during data recording or data reproduction, a focus error signal that indicates how much the laser light is brought to a focus on the data recording surface. Based on the focus error signal, the recording/reproducing apparatus appropriately moves an objective lens of an optical pickup along an optical axis of the laser axis in a direction that closes in on the data recording surface and an opposite direction to thus focus the laser light on the data recording surface of the optical disc.
In the recording/reproducing apparatus, an error may be caused in the focus error signal due to assembly accuracy of the optical pickup (e.g., error in adjusting arrangement position of optical component), molding accuracy of various components constituting the optical pickup, and the like. Therefore, the recording/reproducing apparatus sets, at a time of start-up, for example, a value (constant value) of a lens position correction signal (hereinafter, referred to as “focus bias”) for correcting the position of the objective lens. Further, the recording/reproducing apparatus adds the focus bias to the focus error signal at times of data recording and data reproduction and adjusts the position of the objective lens based on a result of the addition. As a result, even when an error is caused in the focus error signal, the recording/reproducing apparatus corrects the position of the objective lens so as to cancel out the error of the focus error signal by the focus bias to bring the laser light to a focus on the data recording surface of the optical disc.
Moreover, in a case of a high-density optical disc, it is necessary to carry out a spherical aberration correction to deal with a thickness error of a cover layer or a plurality of recording layers in a multilayer structure. Particularly in a recording/reproducing apparatus that includes a lens having high NA, such as a Blu-ray disc, due to a small focus bias/spherical aberration margin, it is essential to carry out a spherical aberration adjustment together with a focus bias adjustment.
As well-known techniques regarding the focus bias adjustment and the spherical aberration adjustment, a method of carrying out a focus bias adjustment and a spherical aberration adjustment at a time of start-up (see, for example, Japanese Patent Application Laid-open No. 2004-95106 and Japanese Patent Application Laid-open No. 2004-241081; hereinafter, referred to as Patent Document 1 and Patent Document 2, respectively), a method of adjusting a focus bias and an aberration by performing sensitivity learning of a focus bias adjustment and an aberration correction during data read and performing a multidimensional search (see, for example, Japanese Patent Application Laid-open No. 2002-342952; hereinafter, referred to as Patent Document 3), and the like are known.
Furthermore, in the recording/reproducing apparatus, it is necessary for an optical axis of light output from the optical pickup to be vertical to a signal recording surface of a disc. Therefore, a tilt adjustment needs to be carried out for adjusting a relationship between the optical axis of the light output from the optical pickup and the signal recording surface of the disc. As well-known techniques regarding the tilt adjustment, a method of adjusting a tilt together with a focus bias and a spherical aberration at a time of start-up, a method of adjusting a tilt together with a focus bias and a spherical aberration during data read (see, for example, Patent Document 3), and the like are known.